Diego E. Gurvich & Pedro Jaureguiberry, Universidad Nacional de Córdoba, Argentina
Cacti are highly relevant across dry ecosystems of America, but studies on the effects of fires on these important plants are scarce. Our study focuses on the giant cactus Trichocereus terschekii from Northwestern Argentina, locally known as cardon. Despite its ecological and social relevance, and the important role of fire as an environmental factor in its distribution range, the effects of fire on this species have not been studied. The prevalence of T. terschekii makes it a key species, determining ecosystem functioning. Previous studies on similar species (e.g. the saguaro) showed high post-fire mortality and sporadic seedling recruitment, linked to wet years. Recruitment of T. terschekii occurs only from seed (asexual reproduction has not been observed). Therefore, if the mortality is high, it would be important to assess the possible recovery of the population from seeds.
We aim to measure post-fire recovery at two nearby sites that burned 18 years apart (in 2003 and 2021), allowing us to assess the short-term effect of fire, and in particular what factors determine survival, as well as the long-term effects. The oldest fire allows us to measure the long-term survival and the growth of individuals, as well as possible recruitment from seed. To do this we will measure 150 individuals in each fire, as well as unburned control sites. We propose to measure several variables that could be related to both short-term survival and long-term recovery, including micro-environmental characteristics (e.g. cover of rocks, bare soil, vegetation, slope angle and orientation), that could relate to fire severity and influence post-fire dynamics.
We expect to have low post-fire survival and also limited recruitment. We believe that our study will be a valuable contribution to the understanding of the post-fire dynamics of cacti and to the design of proper management and conservation strategies in the region. It could also be used to prevent damage in the future and/or to restore burned sites.
Figure 1. Many individuals of T. terschekii fail to survive fire (1a and 1b), while a few survive and resprout (1c and 1d).
Figure 2. Fire intensity is an important factor in determining the post-fire performance of cacti: some are killed by fire (2a) and others survive (2b).
Figure 3. Micro-environmental conditions nearby cacti, such as rock cover, slope and vegetation cover and type, can influence fire dynamics and therefore postfire response of cacti.
Figure 4. The remains of standing shrubs can be used to estimate the severity of the fire.
Preliminary Conclusions as of the start of 2024:
• We observed low survival of T. terschekii exposed to low- and moderate-intensity fires (Figure 5).
• Survival depends on plant size and some microenvironmental characteristics (likely biomass, which is related to severity at the individual plot level).
• Post-fire growth via resprouting was not related to plant size, but rather to the level of damage to the bark, indicating the relevance of remaining photosynthetic tissue after the fire.
• Severity estimated by remote sensing tools, such as the dNBR index, could be useful for improving survival estimates at the landscape level.
Figure 5. The proportion of surviving T. terschekii across the three studied sites
Final Conclusions as of the end of 2024:
Trichocereus terschekii, locally known as “cardón”, is an iconic columnar cactus in the arid regions of northwestern Argentina and southern Bolivia, where it holds a unique socio-cultural and ecological value. In recent years, wildfires have increased their incidence in these regions, raising concern about cardón’s resilience to fire. Our study assessed the impact of fire on T. terschekii by comparing sites with similar environmental conditions but different fire histories: burned in 2017, burned in 2021 and unburned, all located near Cuesta de la Cébila, NW Argentina.
In each site, we recorded mortality, environmental characteristics, and fire intensity indicators, and analyzed post-fire growth patterns. We also measured fruit and seed production, bringing some samples to the lab for weight and germination tests.
The mortality recorded in the burned sites was very high, rounding 80%, aligning with findings for the saguaro (Carnegia gigantea), a similar cactus from the deserts of North America. We found that survival probability declined with fire intensity, while post-fire growth was related to the level of bark damage. Plants with greater damage to the bark (essential for photosynthesis) grew less than those with lower damage.
Preliminary results on the cardon’s reproductive output show that burned plants have much lower fruit and seed production than unburned plants (Figure 8). This, combined with the high post-fire mortality of the species, suggests very limited potential for natural regeneration.
Understanding the biology and ecology of succulent plants in their natural environments is fundamental to developing effective management policies to preserve their populations. Unlike the relatively high post-fire resilience seen in globose cacti, studies on columnar cacti indicate higher sensitivity. These results underscore the need for fire prevention measures in these increasingly fire-prone ecosystems, and suggest that population recovery after fires could benefit from active restoration.
Figure 6. Collecting ripe fruits from Trichocereus terschekii
Figure 7. Details of the fruit of Trichocereus terschekii
Figure 8. A comparison of the number of fruits produced per plant across the three studied sites. Burned plants produces a much lower number of fruits than unburned plants (control).